SKAMP is a 13-item rating scale that measures classroom manifestations of ADHD consisting of 2 subscales (7 items for Attention and 6 items for Deportment) used to generate a score at Hours 10, 11 and 12 on Day 7 of Weeks 1, 2 and 3. The ratings were based on both frequency and quality of specific behaviors. The rating scale is 0 (normal, no impairment) to 6 (maximum impairment) for a total possible combined score of 0 to 78. The reported measure is the difference from baseline of the 2 combined subscores averaged over Hours 10, 11 and 12. A negative score indicates improvement.

SKAMP is a 13-item rating scale consisting of 2 subscales (7-items for Attention and 6-items for Deportment) that measures classroom manifestations of ADHD. SKAMP was used to generate a score on the Attention subscale at Hours 10, 11, and 12 on Day 7 of Weeks 1, 2, and 3. The rating scale is 0 (normal, no impairment) to 6 (maximum impairment) for a total possible combined score of 0 to 42 for the Attention subscale. The reported measure is the difference from baseline of the subscore averaged over Hours 10, 11, and 12. A negative score indicates improvement.

SKAMP is a 13-item rating scale consisting of 2 subscales (7-items for Attention and 6-items for Deportment) that measures classroom manifestations of ADHD. SKAMP was used to generate a score on the Deportment subscale at Hours 10, 11, and 12 on Day 7 of Weeks 1, 2, and 3. The rating scale is 0 (normal, no impairment) to 6 (maximum impairment) for a total possible combined score of 0 to 36 for the Deportment subscale. The reported measure is the difference from baseline of the subscore averaged over Hours 10, 11, and 12. A negative score indicates improvement.

Permanent Product Measure of Performance of Measurement (PERMP) is an age-adjusted, paper-and-pencil math test consisting of 5 pages of 80 math problems each presented in ascending order of difficulty (requiring addition, subtraction, multiplication, and division computations, respectively) during a 10-minute time period. At the end of the 10-minute math test, papers are collected and scored; the number of problems attempted and the number of problems correctly answered are generated as objective measures related to "academic productivity." A positive score indicates improvement.

Permanent Product Measure of Performance of Measurement (PERMP) is an age-adjusted, paper-and-pencil math test consisting of 5 pages of 80 math problems each presented in ascending order of difficulty (requiring addition, subtraction, multiplication, and division computations, respectively) during a 10-minute time period. At the end of the 10-minute math test, papers are collected and scored; the number of problems attempted and the number of problems correctly answered are generated as objective measures related to "academic productivity." A positive score indicates improvement.

Subjects meeting the DSM-IV criteria for primary diagnosis of ADHD-Combined type, or predominantly hyperactive-impulsive subtype, as established by the K-SADS-PL (Kiddie Schedule for Affective Disorders and Schizophrenia-Present and Lifetime Version). If a DSM-IV-defined ADHD diagnosis is difficult to establish due to possible co-morbidity, the subject will not be enrolled into the study.

Subjects should be on a stabilized total daily dose or nearest equivalent of 40-60 mg methylphenidate or 20-30 mg of d-methylphenidate for at least two weeks prior to Screening visit.

Exclusion Criteria:

Subject or subject's guardian unable to understand or follow instructions necessary to participate in the study.

Diagnosed with or history of a tic disorder or Tourette's syndrome.

History of seizure disorder.

The presence of a known medical condition that would preclude the use of methylphenidate.